Radio frequency (RF) transmitters used in various applications emit electrical signals at power levels adequate for maintaining reliable wireless communications. Typical transmitters emit RF radiation more or less uniformly in all directions. This requires a great deal of energy, due to signal attenuation levels and interference occurring over the air in a typical RF transmission environment.
In some cases it is desirable to limit the amount of RF energy levels in surrounding volume and yet still allow a reliable communications channel to specific areas. For example in some circumstances, it may be desirable to reduce interference or lower the amount of power required to communicate in a particular area, which may be far from a radio frequency transmission source, or to penetrate a heavily shielded enclosure. However, current wireless technologies provide a limited useful range.
For these and other reasons, improvements are desirable.